It is estimated that 0.5%-1.0% of the U.S. population has epilepsy, and that 20% of patients with epilepsy have medically refractory seizures. Patients with unilateral temporal lobe seizure onsets have an excellent chance of becoming seizure-free following temporal lobectomy. Based on the successful completion of a Pilot Clinical Trial showing that seizure-free rates were in excess of 80% and with acceptable toxicity, there is equipoise for treating well-selected patients with either radiosurgery or temporal resection. The purpose of this study is to compare the effectiveness of radiosurgery with temporal lobectomy in the treatment of patients with pharmaco-resistant temporal lobe epilepsy including freedom from seizures, seizure reduction, neuropsychological outcomes, quality of life and cost-effectiveness. Aim 1: To compare the seizure-free outcomes and morbidity of Gamma Knife radiosurgery (GKS) for patients with pharmaco-resistant temporal lobe epilepsy with those of open temporal lobectomy. Our primary hypothesis is that radiosurgery and lobectomy will have equivalent seizure-free rates at 25-36 months following therapy (one-year of seizure freedom beginning 2 years after treatment). The two arms will be considered equivalent if a one-sided 95% confidence interval precludes a decrease in seizure-free rate of 15%. Our secondary hypothesis is that radiosurgery will result in significant reductions in seizures compared to baseline and that by 2 years following treatment the percentage reduction in seizures will be identical for these two treatments. Aim 2: To compare the neuropsychological outcomes in patients undergoing radiosurgery and temporal lobe surgery, in particular with respect to verbal memory function for language-dominant hemisphere treated patients. Our hypothesis is that patients treated for speech-dominant temporal lobe seizures with temporal lobectomy will show significant reductions in verbal memory and those patients treated with radiosurgery will not have significant reduction in measures of verbal memory. Aim 3: To determine what changes occur in the quality of life of patients with temporal lobe epilepsy following radiosurgical treatment as compared with open surgery. Our primary hypothesis is that there will be improvements (comparing baseline with 3 years post- treatment) in quality of life measures in both groups. Our secondary hypothesis is that both open surgery and radiosurgery subjects will undergo transient reductions in quality of life measures caused by treatment effects during the first year following treatment, but that quality of life will improve for subjects who become seizure-free, independent of treatment group. Aim 4: To compare the cost-effectiveness of radiosurgery compared with open surgery. We hypothesize that radiosurgery will be cost-effective compared to temporal lobectomy over the lifetime of the patient. The purpose of this study is to compare two methods of treatment of surgically-amenable epilepsy: standard anterior temporal lobectomy versus noninvasive Gamma Knife radiosurgery. Beyond the main outcome of the number of patients rendered seizure-free, we will compare preservation of language functions, quality of life measures, and the cost of treatment. PUBLIC HEALTH RELEVANCE: Pharmaco-resistant epilepsy is a significant health problem for which new therapies are needed. This study is designed to compare traditional surgery (temporal lobectomy) with the novel technique of Gamma Knife radiosurgery in the treatment of patients with temporal lobe epilepsy. This therapy would offer a non-invasive approach to this problem with potential reduction in morbidity (surgical complications, reduced language function). The study is designed to show that this therapy will improve quality of life for patients with epilepsy with reduced complications and cost-savings.